untitled European Journal of Chemistry 5 (1) (2014) 167‐170 European Journal of Chemistry ISSN 2153‐2249 (Print) / ISSN 2153‐2257 (Online)  2014 Eurjchem Publishing ‐ Printed in the USA http://dx.doi.org/10.5155/eurjchem.5.1.167‐170.917 European Journal of Chemistry Journal homepage: www.eurjchem.com SO3H‐Carbon derived from glycerol: An efficient and recyclable catalyst for smooth and regioselective azidolysis of oxiranes in water Vijay Manneganti, Badari Narayana Prasad Rachapudi, and Lakshmi Anu Prabhavathi Devi Bethala * Centre for Lipid Research, CSIR Indian Institute of Chemical Technology, Hyderabad‐500 007, India *Corresponding author at: Centre for Lipid Research, CSIR Indian Institute of Chemical Technology, Hyderabad‐500 007, India. Tel.: +91.40.27191845. Fax: +91.40.27193370. E‐mail address: prabhavathi@iict.res.in (L.A.P.D. Bethala). ARTICLE INFORMATION ABSTRACT DOI: 10.5155/eurjchem.5.1.167‐170.917 Received: 05 September 2013 Received in revised form: 30 October 2013 Accepted: 02 November 2013 Online: 31 March 2014 KEYWORDS A series of β‐hydroxyazides were effectively synthesized from the regioselective ring opening of oxiranes by azide anion in presence of glycerol‐based sulfonic acid functionalized carbon as a novel reusable heterogeneous catalyst in H2O achieving good yields (80‐98%). The workup procedure was simple, and the catalyst could be reused over five times without losing its catalytic activity and selectivity. Water Oxiranes Azidolysis Sodium azide Azidohydrins Carbon acid catalyst 1. Introduction The 1,2‐epoxide functionality is largely present in nature, having biologically important and a powerful building block in organic synthesis [1]. Their inherent polarity and strain, makes susceptible to react with a large number of organic compounds [2‐5]. Ring opening reactions of epoxide with nucleophiles are considered as an interesting approach in organic synthesis of many functionalized oxygenated compounds. The reaction with nucleophiles such as oxygen compounds (Water, alcohols and phenols) [6‐10], nitrogen compounds (Amine, amine deriva‐ tives, azide, nitrate, and isocyanate) [11‐13], halides [14], and various carbon nucleophiles [15] have been performed in both organic and aqueous solvents. Among the numerous products from nucleophilic reactions of epoxide, vicinal azidohydrins [16] exhibit key role in organic synthesis as potential precursors for 1,2‐aminoalcohols which are well known as β‐ blockers and a common structural component in vast group of natural products [11,17‐20], and often used in carbohydrate chemistry or in the chemistry of carbocyclic nucleosides [11,16] can be obtained through the nucleophilic ring opening of epoxides with azide nucleophile [21‐24]. Even though the classic protocol [11,16] uses sodium azide and ammonium chloride, the azidolysis reaction requires long reaction time (12‐48 h) and the azidohydrin is often accompanied by isomerization, epimerization and rearrangement of products. However, the azide opening is promoted by traditional homogeneous systems as metal chlorides [25,26], salts [27] and alkyl metal azides [28‐32]. Some heterogeneous catalysts, relying on the use of traditional solid acids such as amberlite IRA‐400 supported azide [33]. Dowex resin grafted by poly ethylene glycol [34], oxone [35], sodium azide supported on Zeolite CaY [36], ammonium salt of a hetero poly acids [37], quaternized ammonium salt [38] and quaternized amino functionalized cross linked polyacrylamide [39] have been reported. Recently, hot water promoted azidolysis also reported [40]. Most of the reactions suffer from long reaction times, involving organic solvents and elevated temperatures; hence there is a need to develop green, mild, economically viable and eco‐friendly method for the azidolysis of epoxide. In recent years, carbon‐based solid acid catalysts have gained significant attraction over homogeneous catalysts as they are highly efficient, sustainable, and eco‐friendly [41‐45]. In this connection, Prabhavathi et al., reported sustainable method for the preparation of sulfonic acid functionalized carbon (SO3H‐carbon) catalyst having 1.6 mmol/g acid density with surface area of 0.21 m2/g from bioglycerol (Biodiesel by‐ product) and also from the glycerol‐pitch (Waste from fat splitting industry) by the in situ partial carbonization in a single step [46,47]. This catalyst exhibited excellent catalytic properties by demonstrating its effectiveness for various transformations [46‐53] due to its high thermal stability, 168 Manneganti et al. / European Journal of Chemistry 5 (1) (2014) 167‐170 Scheme 1 reusability and strong acid sites of sulfonic acid functional groups. In continuation of our ongoing research in the applications of the glycerol‐based catalyst, we herein report a simple and highly efficient method for the regioselective ring opening of oxirane by azide anion in water (Scheme 1). 2. Experimental 2.1. Materials and methods Chemicals were purchased from S. D. Fine or Sigma Aldrich Chemical Companies. All other reagents and solvents used were of analytical grade. TLC was monitored by using silica gel (SiO2) 60F254 plates (Merck, India). Conversion percentages were studied on Agilent 6850 series Gas Chromatography (GC). Column chromatography was performed by using SiO2, 100‐ 200 mesh, Qualigens, India. IR Spectra was recorded on Perkin Elmer, Model: Spectrum BX, FT‐IR using CHCl3; in cm‐1. 1H and 13C NMR Spectra were recorded on Varian 300, Palo Alto, USA spectrometer at 300 and 75 MHz respectively at 25 °C in CDCl3, δ in ppm relative to Me4Si as internal standard and coupling constant (J) in Hz. Mass spectra was recorded on Waters, Micromass‐Quatromicro electron spray ionization. 2.2. Glycerol‐based sulfonic acid functionalized carbon catalyst [46] A mixture of glycerol (10 g) and concentrated sulphuric acid (30 g) was heated from ambient temperature to 220 °C for 20 min, to facilitate in situ partial carbonization and sulfonation. The reaction mixture was allowed to remain at that temperature for about 20 min (until foaming ceased) to obtain solid carbon material and was cooled to ambient temperature and washed with hot water until the wash water becomes neutral to pH. The partially crystalline product was filtered and dried in an oven at 120 °C for 2 h until it was moisture free to obtain the carbon acid catalyst in ~56% yield (5.60 g). 2.3. General procedure for the synthesis of β‐hydroxyazides Sodium azide (1.2 mmol) was added to the mixture of oxirane (1 mmol), carbon catalyst (2 wt.% of oxirane) in water (1 mL). The suspension was stirred at 90 °C (TLC (hexane:ethyl acetate, v:v, 4:1)). After completion of the reaction, the catalyst was recovered for reuse by simple filtration, and the product was extracted with ethyl acetate (3×5 mL). The extract was dried over anhydrous Na2SO4, and concentrated under vacuum to obtain β‐hydroxyazide. The product mixture was analyzed by GC for the determination of conversion % and the pure product was isolated (80‐98%) by silica gel column chromatographic separation. 2‐Azido‐2‐phenylethanol (1a): FT‐IR (Neat, v, cm‐1): 3369 (OH), 2103 (N3). 1H NMR (300 MHz, CDCl3, δ, ppm): 7.28‐7.38 (m, 5H, Ar‐H), 4.61 (t, J = 6.7 Hz, 1H, CH), 3.67 (d, J = 6.0 Hz, 2H, CH2), 2.33 (s, 1H, OH). ESI‐MS (m/z): 186 (M + Na)+. Trans‐2‐azidocyclohexanol (2b): FT‐IR (Neat, v, cm‐1): 3345 (OH), 2102 (N3). 1H NMR (300 MHz, CDCl3, δ, ppm): 3.25‐3.33 (m, 1H, CHOH), 3.05‐3.14 (m, 1H, CHN3), 2.25 (s, 1H, OH), 1.93‐ 2.02 (m, 2H, CH(OH)CH2), 1.65‐1.74 (m, 2H, CH(N3)CH2), 1.15‐ 1.24 (m, 4H, CH2‐CH2). ESI‐MS (m/z): 164 (M + Na)+. 1‐Azido‐3‐phenoxypropan‐2‐ol (3b): FT‐IR (Neat, v, cm‐1): 3391(OH), 2104 (N3). 1H NMR (300 MHz, CDCl3, δ, ppm): 7.23‐ 7.30 (m, 2H, Ar‐H), 6.86‐6.98 (m, 3H, Ar‐H), 4.10‐4.18 (m, 1H, CH), 3.98 (d, J = 5.2 Hz, 2H, OCH2), 3.46‐3.52 (m, 2H, CH2N3), 2.68 (s, 1H, OH). ESI‐MS (m/z): 216 (M + Na)+. 1‐Azido‐3‐(benzyloxy)propan‐2‐ol (4b): FT‐IR (Neat, v, cm‐1): 3414 (OH), 2102 (N3). 1H NMR (300 MHz, CDCl3, δ, ppm): 7.24‐7.34 (m, 5H, Ar‐H), 4.51 (s, 2H, Ar‐CH2), 3.87 (m, 1H, CH), 3.43‐3.47 (m, 2H, OCH2), 3.28‐3.32 (m, 2H, CH2N3), 2.72 (bs, 1H, OH). ESI‐MS (m/z): 230 (M + Na)+. 1‐Azido‐3‐(cinnamyloxy)propan‐2‐ol (5b): FT‐IR (Neat, v, cm‐1): 3359 (OH), 2101 (N3). 1H NMR (300 MHz, CDCl3, δ, ppm): 7.22‐7.40 (m, 5H, Ar‐H), 6.53 (d, J = 15.8 Hz, 1H, Ar‐CH=CH), 6.22‐6.28 (m, 1H, Ar‐CH=CH), 4.17 (d, 2H, CH=CH‐CH2), 3.94‐ 4.01 (m, 1H, CH), 3.45‐3.56 (m, 2H, OCH2), 3.34‐3.40 (m, 2H, CH2N3), 2.49 (bs, 1H, OH). ESI‐MS (m/z): 256 (M + Na)+. 1‐Azido‐3‐(p‐tolyloxy)propan‐2‐ol (6b): FT‐IR (Neat, v, cm‐1): 3396 (OH), 2103 (N3). 1H NMR (300 MHz, CDCl3, δ, ppm): 7.06 (d, J = 8.3 Hz, 2H, Ar‐H), 6.78 (d, J = 8.3 Hz, 2H, Ar‐H), 4.09‐ 4.17 (m, 1H, CH), 3.97 (d, J = 5.2 Hz, 2H, OCH2), 3.47‐3.52 (m, 2H, CH2 N3), 2.61 (bs, 1H, OH), 2.28 (s, 3H, Ar‐CH3). ESI‐MS (m/z): 230 (M + Na)+. 1‐Azido‐3‐(hexyloxy)propan‐2‐ol (7b): FT‐IR (Neat, v, cm‐1): 3422 (OH), 2102 (N3). 1H NMR (300 MHz, CDCl3, δ, ppm): 3.86 (m, 1H, CH), 3.41‐3.47 (m, 4H, 2 OCH2), 3.31‐3.33(m, 2H, CH2 N3), 2.56 (bs, 1H, OH), 1.56 (quin, 2H, CH2), 1.25‐1.38 (m, 6H, 3 CH2), 0.90 (t, J = 6.4 Hz, 3H, CH3). ESI‐MS (m/z): 224 (M + Na)+. 3. Results and discussion Initially, different solvents like CH3COCH3, CH2Cl2, THF, CH3CN, DMF and H2O were screened for the azidolysis of styrene oxide by treating with 1.2 mmol of sodium azide in presence of 10 wt% of catalyst at reflux temperatures. Among these, only H2O and DMF are found to be suitable for this reaction (Table 1). However, because of DMF’s toxicity, cost, difficulty in removing and possible environmental problems, H2O was preferred as the most suitable solvent. It was investigated to optimize the reaction conditions like H2O content (0.5 to 2 mL), amount of the catalyst (2 to 10 wt% of oxirane) and sodium azide (1 to 2 mmol) for complete azidolysis of styrene oxide (1 mmol) to the corresponding azidohydrin at 90 C. From this study, the optimum conditions were found to be 1.2 mmol of NaN3 and 2 wt% of catalyst in 1 mL of water at 90 °C for 0.5 h. In order to generalize the validity of the protocol, we extended our study towards different oxiranes having activating and deactivating groups (Table 2). Excellent yields of the desired β‐azido alcohols are obtained with a reversal of regioselectivity indicating attack at the less substituted carbon of the aliphatic oxiranes (Entries 2‐7, Table 2), while styrene oxide (Entry 1, Table 2), as an aryl oxirane formed the major product as 2‐azido‐2‐phenylethanol, by the attack of azide nucleophile at the benzylic position, this is due to the formation Manneganti et al. / European Journal of Chemistry 5 (1) (2014) 167‐170 169 Table 1. Effect of solvent on azidolysis of styrene oxide with NaN3 (1.2 mmol) in presence of glycerol‐based SO3H‐carbon catalyst. Solvent Time (min) Temperature Result CH2Cl2 60 reflux No reaction CH3COCH3 60 reflux No reaction CH3CN 60 reflux No reaction THF 60 reflux No reaction DMF 60 reflux Completed H2O 60 90 °C Completed Table 2. Glycerol‐based SO3H‐carbon catalysed ring opening of epoxides with NaN3 (1.2 mmol) in water at 90 °C. Entry R Product a Time (h) Yield (%) b 1 C6H5 1a 0.5 94 2 C6H10 2b 0.5 92 3 C6H5OCH2 3b 1.0 98 4 C6H5CH2OCH2 4b 1.25 90 5 C6H5CH=CHCH2OCH2 5b 4.0 90 6 p‐CH3‐C6H4OCH2 6b 5.0 89 7 C6H13OCH2 7b 5.0 80 a Products were identified by comparison of their physical and spectral data with those of authentic samples. b Isolated yields. of a stable benzyl carbocation during mechanism, is evidenced by electronic factors [25‐40], whereas in the case of aliphatic oxiranes (Entries 2‐7, Table 2), steric factors predominate over electronic factors, thereby facilitating attack at the less hindered carbon atom of the oxirane ring. Furthermore, oxiranes derived from cycloalkenes, such as 7‐oxabicyclo [4.1.0]heptanes (Entry 2, Table 2), reacted smoothly in SN2 fashion to afford the corresponding azidohydrine; and the reaction was completely anti‐sterioselective, thus resulting in trans isomer only. It was further evidenced by coupling constants of the ring H‐atoms in 1H NMR spectrum. All the purified products were characterized by ESI‐MS, IR, 1H NMR data and are in comparison with authentic samples. The admirable quality of the carbon acid catalyst could be the recovery and reusability. After the reaction, the product was extracted into ethyl acetate, catalyst from aqueous layer was separated by simple filtration, washed with MeOH, dried and reused. The reusability study of the catalyst for the azidolysis of of 2‐(phenoxymethyl) oxirane under optimized conditions for five catalytic runs was observed to be no considerable loss of activity of the catalyst and resulted in complete reaction within 1 h in 94‐92% conversions against 99% of fresh catalyst as depicted in Figure 1. Figure 1. Catalyst reusability study. 4. 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